• Noriyuki Yanagawa, Naoko Kawata, Yukiko Matsuura, Toshihiko Sugiura, Toshio Suzuki, Hajime Kasai, Ryosuke Irie, Ken Iesato, Yuji Tada, Nobuhiro Tanabe, Yoichi Suzuki, and Koichiro Tatsumi.
• Department of Respirology, Graduate School of Medicine, Chiba University, Chiba, Japan.
• Acta Radiol. 2015 Apr 1;56(4):438-46.

BackgroundThe estimation of emphysematous changes is very sensitive to computed tomography (CT) threshold level. In clinical practice, the predetermined threshold is usually set at -950 Hounsfield units (HU) for the detection of low attenuation volume (LAV). However, threshold levels that are tightly connected to pulmonary function abnormalities have not been determined.PurposeTo determine the threshold level for calculating an LAV that closely reflects airflow limitation in patients with chronic obstructive pulmonary disease (COPD).Material And MethodsSeventy-six consecutive non-COPD smokers and COPD patients underwent paired inspiratory and expiratory multidetector CT (MDCT). LAV% was segmented every 10 HU between -1000 and -750 HU to examine the correlation between LAV% and indexes of obstructive impairment.ResultsLAV% gradually increased as the threshold level increased on both inspiratory and expiratory images. LAV% on inspiratory images was higher than that on expiratory images at all threshold levels between -1000 and -750 HU. The threshold level that correlated with obstructive impairment differed between the two images: -930 HU on inspiratory and -870 or -880 HU on expiratory images.ConclusionLAV% dramatically changed according to the threshold level on both inspiratory and expiratory images, indicating that LAV% is dependent on the attenuation threshold level in patients with COPD. The threshold linking LAV% to airflow limitation was higher on expiratory than on inspiratory images.© The Foundation Acta Radiologica 2014 Reprints and permissions: sagepub.co.uk/journalsPermissions.nav.

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